With the advancement of information communication technologies, various wireless communication technologies have recently been developed. Among the wireless communication technologies, a wireless local area network (WLAN) is a technology whereby Internet access is possible in a wireless fashion in homes or businesses or in a region providing a specific service by using a portable terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), etc.
The IEEE 802.11n is a technical standard relatively recently introduced to overcome a limited data rate which has been considered as a drawback in the WLAN. The IEEE 802.11n is devised to increase network speed and reliability and to extend an operational distance of a wireless network. More specifically, the IEEE 802.11n supports a high throughput (HT), i.e., a data processing rate of up to above 540 Mbps, and is based on a multiple input and multiple output (MIMO) technique which uses multiple antennas in both a transmitter and a receiver to minimize a transmission error and to optimize a data rate.
As the WLAN is actively propagated and applications employing the WLAN are diversified, a necessity for a new WLAN system for supporting the throughput higher than the data processing speed supported by the IEEE 802.11n standard is on the rise in an STA. The next-generation WLAN system supporting a Very High Throughput (VHT) is the next version of an IEEE 802.11n WLAN system and is one of IEEE 802.11 WLAN systems which have recently been proposed in order to support a data processing speed of 1 Gbps or higher in an MAC Service Access Point (SAP).
The next-generation WLAN system supports the transmission of a Multiple User-Multiple Input Multiple Output (MU-MIMO) scheme in which a plurality of non-AP STAs accesses a radio channel at the same time in order to efficiently use the radio channel. According to the MU-MIMO transmission scheme, an AP can transmit a frame to one or more MIMO-paired non-AP STAs at the same time.
Meanwhile, as the propagation of the WLAN is activated, an environment is appearing where one AP provides service to a large number of non-AP STAs. Furthermore, as mobile devices supporting the WLAN are increased, there is a need for a method of supporting increased mobility.
In order for an AP and a non-AP STA to exchange frames including data in the WLAN, an association procedure must be first performed. If the number of non-AP STAs to be associated with one AP is increased, a very long time is necessary for the association because data exchanged for the association is increased. Furthermore, since the time occupied by a channel for the association procedure is increased, other STAs may be restricted to accessing the channel for traffic processing. Consequently, a current WLAN environment in which an association between an AP and non-AP STAs is frequently generated may not be properly supported owing to increased mobility, and thus the throughput of the WLAN system based on the substantial exchange of data may be deteriorated. Accordingly, there is a need for a communication method in a WLAN system based on an association procedure which is suitable for a new WLAN system environment.